<button class="btn">
  <span class="default-text">New Level Unlocked!</span>
  <span class="hover-text">Congrats!</span>
</button>

<style>
/* From Uiverse.io by jyefu013 - Tags: notification */
.btn {
  padding: 10px;
  border-radius: 5px;
  font-size: 15px;
  background-color: black;
  color: rgb(238, 255, 0);
  position: relative;
  overflow: hidden;
}

.default-text {
  z-index: 1;
}

.hover-text {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  opacity: 0;
  transition: opacity 0.5s ease-in-out;
}

.btn:hover .default-text {
  opacity: 0;
}

.btn:hover .hover-text {
  opacity: 1;
  animation: bounce 0.5s ease-in-out;
}

@keyframes bounce {
  0% {
    transform: scale(1);
  }

  25% {
    transform: scale(1.2);
  }

  75% {
    transform: scale(1.1);
  }

  100% {
    transform: scale(1);
  }
}

.btn:hover::after {
  content: '';
  position: absolute;
  top: -10px;
  left: -10px;
  width: calc(100% + 20px);
  height: calc(100% + 20px);
  border-radius: 50%;
  background-color: rgba(255, 255, 255, 0.5);
  opacity: 0;
  animation: fireworks 1s linear forwards;
}

@keyframes fireworks {
  0% {
    transform: scale(1);
    opacity: 1;
  }

  100% {
    transform: scale(4);
    opacity: 0;
  }
}

</style>
